DIVING AND SURFACING

When the submarine is traveling on the surface, it is operated like any
other boat with one major exception; it has flood ports along the bottom
that are open to the sea. The sea is prevented from filling the ballast
tanks because they are closed at the top, much like holding a drinking
glass upside down under water. There is no place for the air to escape
because vents along the top of the tank are kept closed. The surfaced submarine
maintains positive buoyancy by riding on a bubble captured in the ballast
tanks.

Diagram A represents a submarine on the surface. The main ballast
tanks are filled with air and the center of gravity (G) is above the center
of buoyancy (B). The water displaced (the area within the heavy line) equals
the weight of the submarine. Diagram B represents a submerged submarine.
The ballast tanks are filled with water and the centers of gravity and
buoyancy are reversed. The displaced water, the area inside the pressure
hull, has decreased and the weight of the displaced water now is the same
as or less than the weight of the submarine.

The submarine achieves a dive by opening the vents and allowing the air
to escape and water to fill the ballast tanks. The bow planes are lowered
and angled down to drive the submarine below the surface. Once submerged,
the boat is trimmed, or balanced, by pumping water between trim tanks.
Over-all trim is the process of attaining neutral buoyancy; final trim
is the establishment of fore and aft equilibrium, or zero bubble, with
neutral buoyancy. The submerged submarine is operated at neutral buoyancy
and control of the vessel is obtained by the rudder and the bow and stern
diving planes. A zero bubble should be maintained without excessive angles
on the diving planes. The primary effect of the bow planes is on the depth,
and the primary effect of the stern planes is on the angle of the submarine.

Negative buoyancy for a quick dive is achieved by flooding the negative
tank which is located at the keel slightly forward of the center of the
boat, adding a slight down angle to the submarine. The negative tank is
blown free of water once submerged.

Pressure on the hull increases with depth. The total pressure that the
hull must be able to withstand is measured by the difference between interior
hull pressure and the external pressure at a given depth. When the maximum
depth is passed, the pressure hull will be crushed.